The volvo redblock SOHC is kind of amusing/funny for HGs; seen about every imaginable (maybe, though so many possibilities with all those fluids/passages/dissimilar metals) kind of failure;
-Electrolysis pitted near fire ring/head compromised from corrosive coolant/****ty wiring/multi-metal engine (alum, brass, copper heater core, iron block, oh my!).
-Pitted block (rare & really sucks when that happens).
-Run to the ragged edge of pinging hot a little bit all the time.
-Leaks oil externally very very slowly/old gasket, head not warped or pitted, block not warped or pitted, HG just very very old/dissolved. Usually ~#1 or #4. That's a sneaker.
-Blown between 2 & 3 fire ring, no idea, seen that one repeatedly on N/A nothing special redblocks, mid-cycle 85-87s mostly, couldn't tell ya! The weird one with that is the car went from very slight miss-power-loss-2-holes on that every time I've experienced it extremely rapidly (like, seconds/minutes) with no warning whatever.
-BCP/Big bore 96mm/2.3L engine super delicate.
-Coolant into combustion chamber. Steam cleaned plug, has a miss cold especially or even slight hydro-lock cold (remove plug and let it spit coolant cranking it over to move it into shop), uses coolant slowly, typically), but doesn't exactly lose compression majorly. Weird.
-Massive coolant blown out externally. Rare/higher boost under duress.
-Melted exhaust port/ran way low on coolant/nuclear B230FT overheat.
-Bolts corroded &/or don't hold the torque anymore.
They revised the head alloy a bunch of times and tolerances on block machining for bores/deck leave a good bit to be desired on redblocks.
More ductile alloy in heads later, doesn't crack between valve seats, but more cam-rattly also B230FT and later on averagely neglected oil change redblock that still basically works/has compression.
Getting a little challenging to find a good oil/good coolant never run hot N/A mid-late cycle head where alloy + likely use/abuse is optimal for a used donor.
Or a later '84 SCP head for B21/23 so you can keep the better early timing cover/marks etc and keep it all sealed up from dirt.
Lot of really lousy quality oil late 70s/early 80s w/little-no zync or lead, plenty of penzoil paraffin to sludge up, no synthetics or semi-synthetics widely available yet.
At least it isn't like the bad run of hondas where half the time the block has to come out to be decked/is warped from minor/regular running warm, count your blessings I guess?
Despite having seen many/varied failures, shouldn't be that often in normal use/cared for
Very shotgun data points on the redblock/arises in very different & varied ways.
Hard to nail down like some other cars where it's more consistent/only fails first in one particular way.
But in normal use, doesn't happen that early/often.